In a wide-mouth 1-quart jar, cover 1/2 cup dried mung beans or green lentils with water. Cover the jar with a double layer of cheesecloth and secure with a rubber band. Let stand.
After 24 hours, drain and rinse the beans through the cloth, then drain again.
Store the jar in a dark place on its side, propping up the base so excess water drains onto paper towels. Rinse and drain the beans or lentils twice a day.
After 36 hours, the beans or lentils will grow tails and be ready to eat, but they taste best when the tails are about 1 1/2 times as long as the beans or lentils. Rinse well, cover the jar loosely and refrigerate for up to 3 days.